Scientists are developing a vaccine which they hope will provide an effective way to treat breast cancer.

The secret ingredient is a toxin from the bacterium that causes tetanus - a disease that affects the nervous system.

It is hoped that the treatment will provide an alternative to Herceptin - which although approved for NHS use last week is highly expensive.

The objective of our vaccine is to stimulate the patient's own immune system

Dr Lana Leach

The new treatment, which is currently being tested in clinical trials, is said to be unique in the way it helps women in the advanced stages of breast cancer.

It targets the HER-2 gene which is present in greater amounts than average, or "overexpressed", in many breast cancer patients.

Dr Dana Leach, who has helped to develop the treatment, said: "The objective of our vaccine is to stimulate the patient's own immune system and to see whether we can induce it to launch specific killer cells as well as producing HER-2 specific antibodies.

"Our first objective is to test the safety of the vaccine, but we also want to make a preliminary evaluation of the vaccine's ability to raise an immune response."

Immune response

HER-2 is overexpressed in many tumours, but because it is also expressed at low levels in some normal tissues, the body does not recognise it as foreign and immune cells do not attack it.

The new vaccine, developed by Danish pharmaceutical company Pharmexa, uses DNA coded with the gene sequence for HER-2.

To this is added small, but inactive fragments of the tetanus toxin. This acts as a wake up call to the immune system, stimulating it to respond to HER-2.

The immune system then recognises the overexpressed HER-2 in the cancer cells and attacks it, but ignores the normal tissue because that contains only low levels.

Some 27 patients are taking part in the trial across the UK and Denmark.

Dr Leach said animal tests had shown the vaccine had produced a specific immune response and there had been no adverse side effects.

The team has yet to analyse the results of the UK/Danish trial, which is due to be completed later this year, but they are excited about its potential.

Advanced stages

Dr Leach said: "The initial indications are that it would be suitable for patients in the advanced stages of breast cancer.

"But I would not see it as a preventive vaccine.

"It might be like Herceptin to prolong life expectancy. We hope to show our vaccine is at least as good as if not better than Herceptin."

Dr Leach said the company is also preparing to start clinical trials of a variation to this approach.

Instead of a vaccine that prompts the body's cells to make the necessary protein, the vaccine will be made beforehand in the laboratory and injected directly as a vaccine into the patient.

Details of the vaccine were presented at the European Breast Cancer Conference in Barcelona.